With the development of technology, a touch screen has gradually replaced a mechanical button panel and becomes a new man-machine interaction tool in the field of an electronic device. Among various touch screens, a capacitive touch screen is applied to more and more electronic device due to its higher transmittance, definition, and reliability.
A capacitive touch screen determines whether there is a touch operation according to the change of capacitance on the touch screen. Therefore, when powers up, a capacitive touch screen obtains a reference capacitance value when the capacitive touch screen is not interfered with. The reference capacitance value is used as a reference to detect the change of capacitance on the touch screen, so as to determine whether there is a touch operation on the touch screen.
The prior art records the following two methods for reference capacitance value calibration:
1) If a foreign matter such as a water stain exists on a touch screen when a reference capacitance value is obtained, the capacitance of the touch screen changes once the foreign matter is removed. If the touch screen detects that the duration for maintaining a changed capacitance value exceeds a specific duration, the touch screen forcibly updates the reference capacitance value. However, when the calibration method is adopted, the reference capacitance value may also be updated if a touch screen is touched by a human hand on purpose for a long time, resulting in wrong calibration and a potential operation failure in a normal touch.
2) If a considerable touch area is pressed (for example, by a palm) on a touch screen when a, reference capacitance value is obtained, the capacitance change values detected by the touch screen may be several positive and negative values. When the proportion of positive values to negative values reaches a certain threshold, the touch screen adjusts the reference capacitance value. However, in this calibration method, the proportion of positive changes to negative changes is difficult to define; moreover, the capacitance value of a touch screen may be influenced by a conductor or a charging device near the touch screen. Therefore, this calibration method is neither stable nor accurate.